No. 2304. REPTILIAN CHARACTERS IN MAMMALS— WORTMAN. 



11 



relatively larger than in the latter genus, is flattened and more or less 

 lozenge-shaped; it is pointed at either extremity and broadly grooved 

 upon its superior surface to receive the flattened spatula-shaped 

 processus gracilis of the malleus, which lies in intimate contact with it 

 and runs forward upon it to its anterior extremity. Its anterior 

 pointed extremity ])rojects freely from the bulla in the direction of 

 the 





?^ 



Wl 



upon 



in the adult, and I may say in 

 the early adolescent stage, is 

 firmly coossified with the slender 

 tympanic ring, giving to its an- 

 terior extremity the appearance 

 of a characteristic three-])ronged 

 enlargement. Careful investi- 

 gation, however, shows that it 

 was originally distinct from the 

 tympanic since the longitudinal 

 striae or grain of the latter bone 

 can be seen crossing upon the 

 outer side of the other at almost 

 a right angle. It terminates in 

 a pointed extremity behind, fur- 

 nishing the ]iosterior end of the 

 tympanic above, where it is in 

 intimate relation with the base 

 of the processus gracilis but not 

 attached to it. Upon its outer side it is produced into a more or less 

 distinct blunt projection which lies just behind the postglenoid process 

 of the scjuamosal. 



In the related genus Hylomys this bone has a very similar form and 

 about the same relative i^roportions as in Gymnura; it is likewise 

 firmly coossified with the slender tympanic ring, but perfectly free 

 from the processus gracilis of the maUeus. 



In Erinaceus I have not been able to identif}'^ this element v.'ith 

 certainty from any of the materials I have thus far studied. The 

 processus gracilis is unusually large, broad, fiat, and more or less 

 spatula-shaped at its anterior extremity, where it laps over the 

 expanded tympanic. Parker represents the anterior extremity as 

 divided by a suture in his figure of the embryo,^ and there seem.s to 

 be little doubt that this divided extremity represents a se])arate ossifi- 



FiG. 5. — Gtmnxje.\. Psi. gl. 

 process; Quad., quadrate; 



PANIC EIN'G. X 2. 



-prOC, POSTGLENOID 



Tymp. ring., tym- 



1 Philos. Trans. Royal Soc. London, 1886, vol. 176, pi. 12, fig. 11. 



